>> But if you have actual values rather than just unit types, note that this
>> won't work:
>>>> > instance DeriveType A B where
>> > someDestructor (SomeConstructor _ b) = b
>> I couldn't understand the sentence "actual values rather than unit
> types". What do you have in mind?
I didn't pay attention to the |b| value returned. So what you meant
was that only a constant function will do, not a function that returns
the value |b|.
P.